Recommended Bearing Installation Tolerances CRANKCASE TOLERANCES CRANKSHAFT END CLEARANCE Finish of Main Bores: Shaft Diameter End Clearance • 60-90 micro inches Ra. 2.000”-2.750”(50mm-70mm) .003”-.007”(.075mm-.175mm) Bore Tolerance: 2.813”-3.500” (71mm-88mm) .005”-.009”(.125mm-.225mm) • .001” (.025mm) up to 10.000” (250mm) bore 3.500” or over (89mm or over) .007”-.011”(.175mm-.275mm) Out-of-Round: • .001” (.025mm) maximum if horizontal is larger than CONNECTING ROD TOLERANCES Finish of Rod Bores: vertical • 60-90 micro inches Alignment: Rod Tolerance: • .002” (.050mm) maximum overall misalignment (.001”- • .0005” (.013mm) up to 3.250” (81mm) diameter .025mm for heavy duty or highly loaded engines) • .001” (.025mm) from 3.250”(81mm)to 10.000” (250mm) • .001” (.025mm) maximum misalignment on adjacent diameter bores (.0005”-.013mm for heavy duty or highly loaded Out-of-Round: engines) • .001” (.025mm) maximum if horizontal is larger than CRANKSHAFT TO LERANCES vertical Taper: MAIN BEARING AND CRANKPIN JOURNALS • .0002” (.005mm) up to 1.000” (25mm) length (.0001”- Finish of Journals: .003mm for heavy duty or highly loaded engines) • 15 micro inches Ra or better (10 micro inches Ra or • .0004” (.010mm) for 1.000” (25mm) to 2.000” (50mm) better for heavy duty or highly loaded engines) length (.0002”-.005mm for heavy duty or highly loaded Diameter Tolerance: engines). • .0005” (.013mm) up to 1.500” (38mm) journal • .0005” (.013mm) for 2.000” (50mm) or longer (.0003”- • .001” (.025mm) for 1.500” (38mm) to 10.000” (250mm) .008mm for heavy duty or highly loaded engines) journal Hour-Glass or Barrel Shape Condition: Same as taper Out-of-Round: Parallelism between rod bore and wrist pin hole .001” • .0005”(.013mm) maximum up to 5.000” (125mm) journal (.025mm) in 5.000” (125mm) (.0002”-.005mm for heavy duty or highly loaded engines) Twist .001” (.025mm) in 6.000” (150mm) • Never use a maximum out-of-round journal with a maximum out-of-round bore. CONNECTING ROD END CLEARANCE Taper: Fillets at end of crankpin should not bind on ends of rod • .0002” (.005mm) maximum up to 1.000” (25mm) long bearing, .004” (.10mm) to .010” (.25mm) clearance recom- journal (.0001”-.003mm for heavy duty or highly loaded mended. engines) • .0004” (.010mm) maximum for 1.000” (25mm) to 2.000” (50mm) long journal (.0002”-.005mm for heavy duty or BEARING SPREAD highly loaded engines) Main bearings: .005” (.13mm) to .020” (.50mm) in excess • .0005” (.013mm) maximum for 2.000” (50mm) or longer of crankcase bore diameter journal (.0003”-.008mm for heavy duty or highly loaded Connecting rod bearings: .020” (.50mm) in excess of rod engines) bore Alignment: • .001” (.025mm) maximum misalignment on adjacent OIL CL EARANCE - RESIZED BEARINGS journals (.0005”-.013mm for heavy duty or highly loaded The oil clearance shown in this catalog are for the factory engines) manufactured precision sizes. When installing a resized • .002” (.050mm) maximum overall misalignment (.001”- bearing, adjust the oil clearance shown as follows: .025mm for heavy duty or highly loaded engines) For babbitt and TM-77 copper-lead: • Crankpin and main journals should be parallel within Add .0004” (.010mm) to both low and high limit .001” (.025mm)(.0005”-.013mm for heavy duty or highly For TM-112 copper-lead: loaded engines) Add .0008” (.020mm) to low limit and .0004”(.010 mm) to Hour-Glass or Barrel Shape Condition: Same as taper high limit Oil Holes must be well blended into journal surface. PIN BUSHINGS Resizing: Light Ream: .007”/.015” Bore: .015”/.030” i Engine Bearing Failure & Analysis Guide Accelerated Wear APPEARANCE Wall thickness reduced from original dimension. Bearing surface worn and polished but not smeared, torn or scored. No evidence of heat, no embedded foreign particles. DAMAGING ACTION Grinding and polishing the crankshaft journals produce burrs that are so small that we can’t see or feel them. Not only is it important that the surface finish meet recommended average Ra or better, but it is also important to always grind opposite to rotation and polish in the direction of rotation. Otherwise it is possible for these microscopic burrs to disrupt the oil film and abrade away the bearing surface. POSSIBLE CAUSES 1. Poor journal surface finish. 2. Wear in the presence of adequate lubrication to prevent heat build-up and wiping is caused by peaks in the journal surface finish profile which penetrate the oil film and abrade the bearing. CORRECTIVE ACTION 1. Check journal surface finish for proper average Ra and regrind as needed. 2. If surface finish is acceptable lightly re-polish in the direction of rotation. 3. Install new bearings. 19 Engine Bearing Failure & Analysis Guide.